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Burj Khalifa
1 Emaar Boulevard, Dubai, United Arab Emirates
associated engineer
William F. Baker
Skidmore, Owings & Merrill Inc
Hyder Consulting
date  January 2004 - 4th January 2010
era  Modern  |  category  Building  |  reference  TY210014
The award-winning Burj Khalifa skyscraper in Dubai is currently the world’s tallest building, and its fifth most expensive to construct — and its design is intended to embody the world’s highest aspirations. The concrete and steel structure accommodates a luxury hotel and residential, restaurant, retail and office space, plus observation lounges providing panoramic views.
Dubai is one of the seven Gulf states of the United Arab Emirates (UAE), and city of Dubai is the most populous settlement in the emirates. Among its many remarkable engineering structures, this tower is probably the most famous. It was known as the Burj Dubai during construction but renamed the Burj Khalifa (Khalifa Tower) on its inauguration in honour of the President of the UAE, the ruler of Abu Dhabi, Sheikh Khalifa bin Zayed al Nahyan (b.1948).
The building is Y-shaped in plan with three equal wings springing from a central hexagonal core. The arrangement enables each wing to act as a buttress for the other two, resulting in a structure with lateral and torsional stiffness.
The wings reduce in plan-size with height, each tier slightly displaced in a spiral stepped pattern, reducing the tower’s bulk as it ascends and spreading its huge self-weight loading over a large area. Above the wings, the central core emerges as a column. The form pays homage to the traditional architecture of the region, and elements such as spiral minarets. At the top is a braced structural steel spire more than 200m tall.
The tower's changing profile offers different shapes at every tier, preventing the coalescence of damaging wind vortices around the building. Because the structure is so slender (small foorptint for its height), extensive wind load testing was essential, as were gravity, wind and seismic analyses.
The reinforced concrete walls, link beams, slabs, foundation raft and piles, plus the steel spire, were subjected to rigorous 3D modelling. The digital model contained over 73,500 shells and 75,000 nodes. More than 40 wind tunnel tests and other studies on the frame and façade were carried out in Guelph, Ontario.
The results showed that under lateral wind loading, the building deflections were well below commonly used criteria. Typically, seismic loading did not govern the design of the main tower but did influence the design of the podium and the spire.
However, the construction was beset with challenges, even in a country as wealthy as Dubai. Contractors and specialists from around the world were involved with the project. Many of the site workers were unskilled and spoke neither Arabic nor English. Logistics difficulties resulted in expensive, globally sourced, raw materials being delivered to a site without room for storage.
Foundation excavation began in January 2004, and piling commenced one month later. The 50m deep foundations consist of a reinforced concrete raft supported on concrete and steel friction piles. Geotechnical and seismic investigations and pile load testing were used to develop a detailed (peer reviewed) 3D foundation settlement analysis, predicting the maximum long term settlement as about 80mm.
Another important design consideration was durability. The groundwater at the site is corrosive, with concentrations of chloride (up to 4.5%) and sulphates (up to 0.6%) higher than found in seawater. Anti-corrosion measures used in the foundations included specialist waterproofing, increased concrete cover, corrosion inhibitors in the concrete mix, crack control criteria and a titanium mesh cathodic protection system.
The 3.7m thick raft was constructed in four sections — for the three wings and core — of C50 (cube strength) self-consolidating concrete. Each pour lasted at least 24 hours. Each of the 194 bored cast in situ piles is 1.5m in diameter and approximately 43m long, with a design capacity of 3,000 tonnes. Reinforcement cages were placed in the piles and C60 self-consolidating concrete, containing 25% fly ash and 7% silica fume, poured around them.
In March 2005, construction of the superstructure commenced. Above the foundations, the podium structure anchors the tower to the ground. Here glazed entry pavilions provide access to the basement, concourse, ground floor and Level 1. In essence, the lower floors are occupied by the hotel, the mid-section is residential and the upper floors house corporate suites. The top four floors are used for broadcasting and communications.
As the wings of the building spiral round, load paths through the different floor plates are maintained using a grid system for the whole tower. Columns above are aligned with walls below, easing construction and removing the problems associated with column transfers.
Structural concrete used in the tower ranged from C60 to C80, with mixes designed to carry the extreme pressures generated by the building’s weight. For example, the C80 concrete for the lower part of the structure had a specified Young’s elastic modulus of 43,800N per sq mm at 90 days.
Daytime summer temperatures in Dubai can reach, and sometimes exceed, 50 degrees Celsius — far too hot to cast concrete without incurring detrimental cracking. Instead, concrete pours were carried out at night, when the air is cooler and more humid. On particularly hot nights, crushed ice was added to the concrete mix to maintain a steady temperature.
During construction, the concrete floor slabs in Levels 5 to 15 exhibited sagging and had to be strengthened with carbon fibre strips and steel I-beams. It has been reported that these floors were designed as prestressed concrete but were poured as simply reinforced concrete, and as a result were too shallow and under reinforced for the loading on them.
The tower contains seven ‘mechanical floors’ to provide the electricity sub-stations, water tanks and pumps, air-handling units and other plant necessary for the smooth operation of the tower’s systems and the comfort of its users. They are located on Levels 17-18, 40-42, 73-75, 109-110, 136-138, 155 and 160-163.
Sets of outriggers at the mechanical floors allow the columns to participate in the lateral load resistance of the structure. The outriggers tie all the vertical load carrying elements together, ensuring uniform gravity stresses and reducing differential creep.
In June 2006, the tower reached Level 50 and by May 2007, it had grown to Level 130. When the tower was up to Level 135, the average foundation settlement was measured as 30mm — well within the movement predicted. On 21st July 2007, Burj Khalifa reached Level 141 and became the world’s tallest building when it rose above the 508m high Taipei 101 tower in Taiwan (completed 2004), previously the tallest.
In September 2007, the tower was at Level 150, bypassing the CN Tower in Toronto (1976) to become the world’s highest free-standing structure. On 8th November 2007, concrete was pumped to a world record height of 601m at a pressure of almost 20N per sq mm, and the building kept on growing.
On 7th April 2008, it reached 629m (Level 160), and became the world’s tallest manmade structure to date, overtaking the KVLY-TV Mast in North Dakota (completed 1963). It topped the record for the tallest manmade structure ever built on 1st September 2008, when it surpassed the previous record-holder, the Warsaw Radio Mast in Konstantynów, Poland (completed 1974, collapsed 1991).
Burj Khalifa’s telescopic spire was constructed inside the building and jacked to its full height using a hydraulic pump. It houses communications equipment and contains more than 4,000 tonnes of structural steel. The spire was completed in January 2009, and marked the topping out of the building. On a clear day it can be seen from 95km away.
The tower’s curtain wall façade consists of reflective glazing panels with aluminium and textured stainless steel spandrels and vertical stainless steel tubular fins. More than 24,000 panels of glass were hand cut individually to clad its exterior. Cladding work was completed in September 2009.
Fire safety and speed of evacuation are vital to the tower’s design. The fire engineering scheme allows for the evacuation on foot of 35,000 people, or more than twice the building’s anticipated occupancy. It’s a long walk to the ground — 2,909 steps — so pressurised air-conditioned refuge areas are provided every 25 floors so people can rest or await rescue. To keep any fires contained, firestops in the form of mineral wool sprayed with fire-retardant mastic are used to plug the gaps between floor slabs and external cladding.
The tower has 57 elevators and 8 escalators. Its building/fire services elevator is the world’s tallest service elevator and has a capacity of 5.5 tonnes. The observatory elevators feature double-deck cabs with space for 10-14 people per cab, and travel at 10m per second.
The outside of the tower can be accessed, for window washing and façade maintenance, from 18 permanent installations. Track-mounted units, stored in garages within the structure, are not visible when not in use and have extending jibs with a maximum reach of 36m. Manned cradles can be deployed from the top of the tower down to Level 7. With all building maintenance units in operation, it normally takes three to four months to clean the exterior.
The public areas inside feature glass, stainless steel, polished stone, silver travertine and stone flooring and Venetian stucco walls. The tower and surroundings contain over 1,000 pieces of artwork, many of them commissioned especially for the project.
On 4th January 2010, on the fourth anniversary of his accession, Burj Khalifa was opened by Dubai’s ruler, Sheikh Mohammed Bin Rashid Al Maktoum (b.1949). At 828m, it is 320m — an astonishing 63 percent — taller than Taipei 101.
Burj Khalifa also holds the record for the height to tip of mast (829.8m) and the highest occupied floor (584.5m). Its observation deck is the second highest in the world at 452.1m, only 22m lower than that of the Shanghai World Financial Center (completed 2008) at 474m. It has the greatest number of floors — 163 — a record held previously by the former World Trade Center Towers in New York, with 110 floors.
The tower took some 22 million man hours to construct and at the peak 12,000 workers were on site every day. It cost £958 million to build, less than half that of the world’s most expensive skyscraper, New York's One World Trade Center (opened November 2014).
Burj Khalifa contains 330,000 cu m of concrete, 68,000 tonnes of cabling, 39,000 tonnes of steel (including 31,400 tonnes of rebar), 103,000 sq m of glass and 15,500 sq m of embossed stainless steel cladding. Its water system supplies an average of 946,000 litres of water daily to occupants. Its peak electrical demand is 36MW.
The tower is surrounded by 11 hectares of urban landscaping, including six water features, extensive gardens and walkways lined with palm trees. The planting is irrigated with water recycled from the building's condensation collection system, which is fed into a tank in the basement car park and yields 68 million litres annually.
Under UAE law, the Contractor and the Engineer of Record are jointly and severally liable for the performance of Burj Khalifa. On 10th March 2010, the Council on Tall Buildings and Urban Habitat (established 1969) officially certified Burj Khalifa as the world’s tallest building.
Developer: Emaar (UAE)
Engineer of record: Hyder Consulting Ltd
Architect: Skidmore, Owings & Merrill LLP (Chicago)
Project manager: Turner International
Wind engineering: RWDI
Fire engineering: Rolf Jenson & Associates
Contractor: Samsung joint venture (Samsung C&T Corporation [South Korea], Arabtec [UAE], Besix [Belgium]
Formwork: Doka
Concrete suplly: Unimix
Concrete pumping: Putzmeister
Cladding: Arabian Aluminium and Far East Aluminium joint venture
Elevators: Otis
Landscaping: SWA Group
Research: ECPK
bibliography
"Burj Khalifa — a new high for high-performance concrete" by Dr James Aldred, Civil Engineering, Vol.163, pp.66-73, London, May 2010
http://burj-khalifa.readabout.org
www.aboutcivil.org
www.burjkhalifa.ae
www.great-towers.com
www.nce.co.uk
www.skyscrapercenter.com
www.som.com
www.thedubaimall.com
Location

Burj Khalifa